Catalytic absorbent and a method for its preparation

ABSTRACT

A novel catalytic absorbent composition is prepared with a synthetic copper or silver carbonate-containing material. The absorbent is useful for removing hydrogen sulfide and mercaptan sulfur from hydrocarbon oils, especially from feedstreams to a reformer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a catalytic absorbent composition, itspreparation, and use for desulfurizing hydrocarbon oils, and mostparticularly to the use of the composition for desulfurizing reformerfeedstocks.

2. Description of the Prior Art

Catalysts containing sulfur-sensitive Group VIII metal components areoften employed in petroleum refining processes such as hydrocracking,synthesis gas processing, methanation, reforming, steam reforming,hydrogenation, and the like. Such catalysts lose their catalyticactivity and stability due to deleterious effects of sulfur duringprocessing. In a typical reforming process treating a straight runnaphtha or cracked naphtha, the feedstock is upgraded (as by increasingthe octane number of the gasoline fraction) by contact with a catalystcomprising a noble metal on alumina. Conditions utilized in reformingprocesses vary depending upon such factors as the type of feed processedand the desired increase in octane level.

To achieve maximum run lengths and increase process efficiency, it isgenerally recognized that the sulfur content of the feedstock must beminimized. Reforming catalysts, and particularly those comprisingplatinum, and even more particularly comprising platinum and rhenium,deactivate rapidly and are even poisoned in the presence of sulfurcompounds. As a result, it is necessary to reduce the sulfur content ofreformer feedstocks as low as possible. Preferably, feedstocks contactedwith reforming catalysts are desulfurized to contain less than about 0.5ppmw sulfur.

A common method of treating reformer feeds to reduce the sulfur contentis by hydrodesulfurization wherein a naphtha or other hydrocarbonfeedstock is contacted with a sulfur-tolerant hydrogenation catalyst inthe presence of hydrogen. Although good sulfur removal may be achievedby hydrodesulfurization units operating under severe conditions, theefficiency of such processes is ultimately limited by equilibrium and/orkinetic considerations. In many instances, it is not possible to obtainhydrodesulfurized products containing less than 0.1 ppmw sulfur asdesired in most reforming operations. Furthermore, it is impossible toguard against occasional upsets in the hydrodesulfurization unit whichcan result in higher than desired levels of organosulfur compoundsremaining in the reformer feedstock.

In addition to hydrodesulfurization, there are other processes employingcatalytically active materials for removing sulfur from hydrocarbons.Such processes reduce the sulfur content of the hydrocarbon by"absorbing" sulfur therefrom and generally employ a catalytically activeabsorbent material under nonhydrogenative conditions. Typically,nonhydrogenative conditions include contact of the absorbent materialwith the feedstock in the absence of hydrogen; however, if desired,hydrogen is sometimes present, but only in amounts or under conditionsthat prevent essentially any hydrogenation of the organosulfurcomponents in the feedstock. Usually, the absorbent material contains ametal component, such a nickel, copper, or silver, and the feedstocksgenerally treated are reformer feedstocks, particularly naphthas.Typical of such processes include that disclosed in U.S. Pat. No.2,755,226 to Annable wherein a bed of copper molybdate pellets isutilized to reduce the sulfur content of naphthas. Similarly, in U.S.Pat. No. 4,224,191 to Bishop III, the use of copper components supportedin conventional carriers is disclosed for reducing the sulfur content ofreformer feedstreams. However, the search continues for catalyticallyactive absorbent materials which are more active and which have morecapacity for the absorption of sulfur than the materials of the priorart.

Accordingly, it is an object of the present invention to provide a novelcomposition useful for desulfurizing hydrocarbon oils.

It is a further object of the present invention to provide a method forpreparing a composition useful for desulfurizing hydrocarbon oils.

Another object of the present invention is to provide a process forupgrading a hydrocarbon oil by contact with a novel composition of thepresent invention.

These and other objects and advantages of the invention will becomeapparent from the following description.

SUMMARY OF THE INVENTION

The present invention relates to a novel catalytic composition preparedwith a synthetic copper or silver carbonate-containing material and to aprocess utilizing such a catalytic composition for upgrading ahydrocarbon oil. In one embodiment, a catalytic absorbent composition isprepared by admixing a precursor of a refractory oxide support with asynthetic copper or silver carbonate compound that is prepared from asoluble copper or silver compound and a soluble carbonate compound. In apreferred embodiment, a catalytic absorbent composition is prepared withalumina and a synthetic basic copper(II) carbonate [CuCO₃ Cu(OH)₂ ] andutilized to remove sulfur, especially hydrogen sulfide and mercaptansulfur, from a hydrocarbon reformer feedstock.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a composition prepared with a materialcontaining a "synthetic" copper or silver carbonate compound. A"synthetic" copper or silver carbonate used herein is prepared fromcopper or silver salts, and not obtained from a silver or coppercarbonate-containing material found in nature.

It will be understood that the "catalytic absorbent" referred to herein,although useful for removing sulfur from hydrocarbon oils, may also, incertain processes, function as a catalyst for promoting hydrocarbonconversion reactions.

It will be further understood that, although the term "catalyticabsorbent" or "catalytic sorbent" is used herein to describe thematerial of the present invention with which the hydrocarbon oils arecontacted, and the term "absorbed" is used to describe the mechanism bywhich the sulfur is held thereon, the invention embraces whatevermechanism, including adsorption, absorption, deposition, chemicalreactions, etc., or some combinations of such mechanisms, by which thesulfur is removed from the hydrocarbon oil and retained by the catalyticabsorbent. Also, the terms "sulfur" and "organosulfur compounds" areused interchangeably herein and are intended to include sulfur inwhatever form, elemental or combined, it may be present.

A catalytic absorbent of the invention comprises synthetically-derivedcopper or silver metal components composited with a porous refractoryoxide. The copper or silver components are usually present in thecatalytic absorbent from about 1 to about 75, preferably about 5 toabout 30, and most preferably about 10 to about 20 weight percent,calculated as the metal. Preferred catalytic absorbents comprise coppercomponents with an alumina-containing refractory oxide support. Copperoxide, derived from a synthetically prepared basic copper(II)carbonate-containing material and composited on a porous refractoryoxide containing gamma alumina, is the most preferred catalyticabsorbent.

Numerous porous refractory oxides may be utilized to support the metalcomponents. Representative of such supports include alumina, silica,silica-alumina, zirconia, silica-zirconia, titania, and magnesia, andcombinations thereof. However, the preferred support is alumina, mostpreferably gamma alumina having a surface area above about 100 m² /gm,with the most preferred surface areas being between 150 and 400 m² /gm.The refractory oxide usually comprises at least about 25 weight percentand preferably at least about 35 weight percent of the catalyticabsorbent.

Synthetic copper and silver carbonate-containing compounds used inpreparing catalytic absorbent compositions of the invention aretypically produced from the reaction of a copper or silver salt combinedwith a carbonate-containing material or a precursor thereof. Forexample, an aqueous solution of a copper or silver salt may be combinedwith a soluble carbonate compound to produce a copper or silvercarbonate-containing precipitate which is separated, washed, and dried.Another typical preparation includes the step of bubbling carbon dioxide(CO₂) gas into a solution of copper or silver salt.

A preferred synthetic carbonate-containing compound is basic copper(II)carbonate [CuCO₃ Cu(OH)₂ ] that is ordinarily prepared by combining asoluble copper salt such as copper(II) nitrate [Cu(NO₃)₂ ] with asoluble carbonate solution, such as an alkali carbonate, i.e., sodiumcarbonate (soda ash), potassium carbonate, and the like.

An unusual feature of the synthetic copper or silvercarbonate-containing material used in the preparation of the catalyticabsorbent is the sulfur content. The synthetic carbonate-containingmaterial ordinarily contains less than about 0.2, preferably less thanabout 0.1, and most preferably less than 0.05 weight percent of sulfur,calculated as S. Furthermore, the atom ratio of sulfur to copper orsulfur to silver metal in the synthetic carbonate-containing material isusually less than about 0.007, preferably less than about 0.005, andmost preferably less than 0.002. As set forth hereinafter in Example I,catalytic absorbents of the invention, prepared with synthetic coppercarbonate-containing materials having less than 0.2 weight percent ofsulfur and a sulfur to metal atom ratio less than 0.007, demonstratesuperior sulfur-absorbing activity and capacity as compared to catalyticabsorbents prepared with a copper carbonate-containing compound obtainedfrom nature and having greater than 0.2 weight percent of sulfur and asulfur to copper ratio greater than 0.007.

A method by which the copper or silver metal components may becomposited with the refractory oxide is comulling. In comulling, theprecursors of the refractory oxide support material are admixed withprecursors of the active metal components, either in solid form or insolution, to produce a paste suitable for shaping by known methods,e.g., pelleting, extrusion, etc. For instance, a precursor of arefractory oxide may be admixed with a synthetic copper or silvercarbonate-containing material along with sufficient liquid, such aswater, until an extrudable paste is formed. More particularly, analumina powder, such as boehmite, is comulled with a synthetic basiccopper(II) carbonate-containing material in the presence of sufficientwater to create a paste extrudable through a die. Ordinarily, theprecursor of the porous refractory oxide is not peptized.

Composites of the synthetic copper or silver carbonate-containingmaterial and refractory oxide prepared by a foregoing method or anobvious equivalent are dried and then calcined at temperatures greaterthan about 500° F., preferably between 600° and 1000° F., and yield acatalytic absorbent containing the active metals in their respectiveoxide forms.

A catalytic absorbent of the invention has a maximum cross-sectionaldimension of the particle from about 1/40 to about 1/4 inch, andpreferably about 1/32 to about 1/6 inch. Although the particles may haveeither a symmetrical or unsymmetrical cross-sectional shape, it ispreferred the particles have a symmetrical cross-sectional shape, suchas a cylindrical or polylobal shape.

Physical characteristics of the catalytic absorbent include a surfacearea generally greater than about 100 m² /gram, and preferably fromabout 200 m² /gram to about 400 m² /gram, as determined by the B.E.T.method. The total pore volume of the absorbent is usually about 0.3 toabout 0.8 cc/gram, as determined by conventional mercury porosimetrytechniques. The compacted bulk density (CBD) of the absorbent is usuallyin the range from about 0.4 to about 0.9 grams/cc.

An unusual feature of the invention is that, in comparison to catalyticabsorbents containing copper or silver metal components prepared fromnon-synthetic carbonate compounds, the catalytic absorbent of theinvention is substantially more active for removing sulfur compoundsfrom a hydrocarbon oil. The synthetic copper and silver carbonatecompounds used in the preparation of the absorbent, therefore,substantially enhance the activity of the absorbent for absorbing sulfurcompounds. In comparison to a similar catalytic absorbent containing nosynthetic copper or silver carbonate compounds, the catalytic absorbentof the invention exhibits at least 25 percent greater, and often morethan 50 percent greater capacity for absorbing sulfur as the comparisonabsorbent. Thus, when reformer feeds and the like are treated for sulfurremoval, the catalytic absorbent of the invention, due to its increasedactivity and capacity for absorbing sulfur, is useful for maintaining alow total sulfur concentration in the product, usually below 0.5 ppmwand preferably less than 0.2 ppmw of hydrogen sulfide and mercaptansulfur, for a time period substantially in excess of that possible withsimilarly prepared catalytic absorbents but containing no metals derivedfrom synthetic copper or silver carbonate compounds.

Another unusual property of the catalytic absorbent of the invention isits sulfur-absorbing capacity under conditions of elevated temperature.The sulfur-absorbing capacity of the absorbent, as determined in weightof absorbed sulfur per weight of fresh catalytic absorbent, issubstantially greater at a higher temperature. The absorbent of theinvention exhibits more than a 25 percent increase in capacity as aresult of an increase in the operating temperature by 100° F. and, asshown hereinafter in Example II, the absorbent exhibits more than 100percent increase at the higher temperature.

After a catalytic absorbent of desired chemical and physicalcharacteristics is prepared, it is usually employed as either a fixed,slurried or fluidized bed of particulates in a suitable reactor vesselwherein a hydrocarbon oil to be treated is introduced and subjected toconditions of elevated pressure and elevated temperature and, in thecase of hydroprocessing, also subjected to a hydrogen partial pressure.The absorbent is preferably used in the absence of added hydrogen.

The catalytic absorbent may be employed in any of several hydrocarbonconversion processes wherein catalytic composites containing copper orsilver metals are known to be catalytically effective. Typical processesinclude dehydrogenation, desulfurization, hydrodesulfurization,oxidation, denitrogenation, demetallization, isomerization, cracking,hydrocracking, reforming, and the like.

The term "hydrocarbon conversion" is intended to include all reactionswherein hydrocarbons change physical or chemical composition. Thehydrocarbons include all forms, such as aliphatic, cycloaliphatic,olefinic, aromatic--including alkaryl and arylalkyl aromatic compounds,in addition to organometallic, organonitrogen, and organosulfurcompounds, particularly those found in conventional hydrocarbon oils.

The conditions employed to upgrade a hydrocarbon oil will vary widelydepending upon the process in which the absorbent is used and the natureof the oil. Most usually, the catalytic absorbent is maintained as afixed bed with the feedstock passing downwardly therethrough, and thereactor is generally operated under conditions including a temperaturefrom about 50° F. to about 1000° F., preferably about 250° F. to about450° F., a pressure from atmospheric to about 3,000 p.s.i.g., preferablyabout 100 to about 2,500 p.s.i.g., and a space velocity of about 0.05 toabout 25, preferably about 3 to about 15 LHSV. During hydroprocessing,the hydrogen recycle rate is usually about 1,000 to about 15,000, andpreferably about 3,000 to about 10,000 standard cubic feet per barrel(scf/bbl).

The absorbent of the invention is particularly effective fordesulfurization reactions, and especially for treating sulfur-containinghydrocarbons to be fed to a reaction vessel having a Group VIIImetal-containing catalyst that promotes hydrocarbon conversion reactionssuch as hydrocracking, methanation, reforming, steam reforming,hydrogenation, including aromatic saturation, and synthesis gasprocessing. Hydrocarbon feedstocks often contain sulfur, largely in theform of organosulfur compounds, such as mercaptans, disulfides, and thelike. These organosulfur compounds are usually present in a totalconcentration greater than 5 ppmw, and often in a concentration inexcess of 10 ppmw, calculated as S. The absorbent is highly effectivefor removing sulfur in the form of hydrogen sulfide and mercaptansulfur.

Contemplated for treatment by the process employing the composition ofthe invention are hydrocarbon-containing oils, herein referred togenerally as "oils," including broadly all liquid, gaseous, andliquid/gaseous hydrocarbon mixtures such as crude petroleum oils andsynthetic crudes. Among the typical oils contemplated are distillatehydrocarbon fractions derived from petroleum, shale oil, liquid coal,oils from bituminous sands, and other synthetic or natural sources.Examples of oils include solvent naphthas, kerosene, diesel fuels, jetfuels, aromatics, heavy naphthas, light naphthas, cycle oils fromcracking operations, coker distillates, cracked gasoline, lubricatingoils, waxes, vacuum fractions, decant oils, reformer feeds, and thelike. It is preferred that the oils contain sulfur components, such asorganosulfur components and hydrogen sulfide, and particularly thoseoils in which the organosulfur compounds comprise mercaptans.

The absorbent is highly suitable for treating reformer feedstocks to besubjected to catalytic reforming over a platinum or platinum-rheniumreforming catalyst or other metal-containing reforming catalyst thatdeactivates upon contact with sulfur. Such feedstocks usually containabove about 0.1 ppmw mercaptan sulfur and boil in the range of 150° to450° F. A preferred reformer feedstock is a naphtha containingorganosulfur compounds essentially completely in the form of mercaptansand hydrogen sulfide. Such a feedstock preferably contains between 0.1and 20 ppmw sulfur in mercaptan form and hydrogen sulfide.

In accordance with a highly preferred process of the invention forremoving sulfur from a hydrocarbon oil, an oil containing less thanabout 10 ppmw of hydrogen sulfide and mercaptan sulfur is contacted withthe catalytic absorbent in a suitable reactor vessel under conditions ofelevated temperature, preferably between 100° and 600° F., and mostpreferably between about 200° and 450° F., of elevated pressure,preferably about 100 to about 600 p.s.i.g., and at a space velocity ofabout 1 to about 20 LHSV. Preferably, contact of the absorbent with theoil is performed in the absence of hydrogen. However, hydrogen may bepresent, but preferably only in amounts or under conditions that preventessentially any sulfur removal from the catalytic absorbent.

The invention is further illustrated by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention defined by the appendedclaims.

EXAMPLE I

A catalytic absorbent A of the present invention is prepared as follows:

One hundred eighty (180) grams of spray-dried alumina powder (boehmite)are dry-mulled for 40 minutes with 42.1 grams of synthetic basiccopper(II) carbonate [CuCO₃ Cu(OH)₂ ] obtained from Shepherd ChemicalCompany and with 2.0 grams of methylated cellulose (Methocel™). Thesynthetic basic copper(II) carbonate material has a sulfur content lessthan about 0.05 weight percent, calculated as S, and a sulfur-to-copperatom ratio less than 0.002. One hundred eighty-eight cubic centimeters(cc) of distilled water are then added and the resultant mixture mulledfor another 60 minutes until an extrudable paste is formed. The paste isextruded through a die having an opening resembling the shape of athree-leaf clover. The resultant extrudates, having cross-sections ofabout 1/16 inch, are dried for 1 hour at 250° F. and calcined for 16hours at 900° F.

A reference catalytic absorbent B is prepared in the same manner ascatalytic absorbent A, except the basic copper(II) carbonate [CuCO₃Cu(OH)₂ ] is naturally occurring malachite. This basic copper(II)carbonate material is found in nature and has a sulfur content of about0.23 weight percent, calculated as S, and a sulfur-to-copper atom ratioof 0.008.

After calcination, the resultant catalytic absorbents A and B each havea nominal composition of 15 weight percent copper components, calculatedas Cu, and a balance of gamma alumina. The surface area of eachcatalytic absorbent is about 300 m² /gram.

Each catalytic absorbent is tested as a sulfur absorbent in thefollowing manner: The catalytic absorbent is placed as a fixed bed in atubular reactor and a hydrocarbon oil containing iso-octane spiked withn-butyl mercaptan to contain 220 ppmw sulfur is passed downwardlythrough the reactor at a space velocity of 5.0 LHSV, at a temperature of300° F., and a pressure of 500 p.s.i.g. The reaction is conducted in theabsence of additional hydrogen (H₂).

Samples of the product are removed from the reactor at 4-hour intervalsover a time period of 44 hours and analyzed by appropriate X-rayfluorescence methods to determine their sulfur concentrations. Theresults of these tests are summarized in TABLE I:

                  TABLE I                                                         ______________________________________                                                   Effluent Sulfur Concentration (ppmw)                                            Catalytic  Catalytic                                             Time, Hrs    Absorbent A                                                                              Absorbent B                                           ______________________________________                                         4           <5         <5                                                     8           <5          5                                                    12            9          23                                                   16            19         58                                                   20            31         83                                                   24            48        105                                                   28            72        131                                                   32            79        142                                                   36           110        153                                                   40           129        176                                                   44           153        --                                                    ______________________________________                                    

As shown, the effluent from the reactor containing catalytic absorbent Aof the invention exhibits detectable sulfur after approximately 12hours, while the effluent from the reactor containing referencecatalytic absorbent B exhibits detectable sulfur after onlyapproximately 8 hours. Even after 40 hours, catalytic absorbent A stillexhibits absorption of approximately 40 percent of the feedstock sulfurwhereas comparative absorbent B only absorbs approximately 20 percent ofthe sulfur in the feed. Thus, the results indicate that preparing acatalytic absorbent with synthetic basic copper(II) carbonatesubstantially increases the capacity of the absorbent for removingsulfur in comparison to a similar absorbent prepared with basiccopper(II) carbonate obtained from naturally occurring malachite.

EXAMPLE II

Portions of catalytic absorbent A of Example I are tested in four (4)experimental runs for sulfur-absorbing capacity with portions of thesame feedstock and at the same conditions as in Example I, except forvariation in the temperature.

Experimental runs 1 through 4 are performed at temperatures of 250° F.,300° F., 350° F., and 400° F., respectively. The data is summarized inTable II:

                  TABLE II                                                        ______________________________________                                        Run       Temp., °F.                                                                       Relative Capacity*, %                                     ______________________________________                                        1         250       ˜40                                                 2         300       100                                                       3         350       170                                                       4         400       265                                                       ______________________________________                                         *Determined in weight of absorbed sulfur per weight of fresh catalytic        absorbent A at 25 percent breakthrough of sulfur in the effluent.        

As shown, at sulfur-absorbing conditions including temperatures at 350°F. and 400° F., catalytic absorbent A demonstrates a respectivesulfur-absorbing capacity that is 70 and 165 percent greater than thatat 300° F. Furthermore, as compared to sulfur-absorbing conditionsincluding a temperature of 250° F., catalytic absorbent A exhibitssubstantially greater sulfur-absorbing capacity at the conditions ofhigher temperature.

Although particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made, and it is intended toinclude within this invention any such modifications as will fall withinthe scope of the invention as defined by the appended claims.

We claim:
 1. A method for preparing a composition comprising admixing asynthetic basic copper carbonate or silver carbonate having a sulfurcontent less than about 0.05 weight percent calculated as S, with aporous refractory oxide, or precursor thereof, forming an extrudablepaste, shaping said extrudable paste, drying the shaped extrudablepaste, and calcining the dried shaped extrudable paste to form a productcomprising copper or silver components and said porous refractory oxide.2. The composition defined in claim 9 wherein said porous refractoryoxide comprises alumina and said product contains about 1 to about 75weight percent of said copper or silver components, calculated as themetal.
 3. The method defined in claim 1 wherein said synthetic basiccopper carbonate comprises basic copper (II) carbonate.
 4. The methoddefined in claim 2 wherein said porous refractory oxide comprisesalumina and said product contains about 1 to about 75 weight percent ofcopper or silver components, calculated as the metal.
 5. The methoddefined in claim 1 wherein said admixing comprises comulling and saidprecursor of said porous refractory oxide is not peptized.
 6. The methoddefined in claim 1 wherein said synthetic basic copper carbonate orsilver carbonate is prepared from a soluble copper or silver salt and asoluble carbonate compound.
 7. The method defined in claim 6 whereinsaid soluble copper salt is copper(II) nitrate and said solublecarbonate compound is selected from the group consisting of alkali metalcarbonates and carbon dioxide.
 8. The method defined in claim 1 whereinthe atom ratio of sulfur to copper or sulfur to silver metal in saidsynthetic copper carbonate or silver carbonate is less than about 0.002.9. A composition comprising copper oxide or silver oxide and a porousrefractory oxide prepared by a method comprising admixing a syntheticbasic copper carbonate or silver carbonate having a sulfur content lessthan about 0.05 weight percent calculated as S, with said porousrefractory oxide or precursor thereof, forming an extrudable paste,shaping said extrudable paste, drying the shaped extrudable paste, andcalcining the dried shaped extrudable paste to form said composition.10. The composition defined in claim 9 wherein said synthetic basiccopper carbonate comprises basic copper (II) carbonate.
 11. Thecomposition defined in claim 9 wherein said porous refractory oxidecomprises gamma alumina.
 12. The composition defined in claim 9comprising about 5 to about 30 weight percent of copper components,calculated as Cu.
 13. The composition defined in claim 9 having asurface area greater than about 100 m² /gram.
 14. The compositiondefined in claim 9 wherein the atom ratio of sulfur to copper or sulfurto silver metal in said synthetic basic carbonate copper or silvercarbonate is less than about 0.002.
 15. The composition defined in claim9 wherein said admixing comprises comulling and said precursor of saidporous refractory oxide is not peptized.
 16. The composition defined inclaim 9 wherein said synthetic basic copper carbonate is prepared from asoluble copper salt and a soluble carbonate compound.